Store glyph bounds in WordMeasurement to avoid slow path width calc

Source/core/layout/line/GlyphOverflow.h

+// Copyright 2015 The Chromium Authors. All rights reserved.

[eae, 2015/06/11 18:33:38]

Retain copyright from Font.h where this came from.

[Xianzhu, 2015/06/11 20:40:09]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef GlyphOverflow_h
+#define GlyphOverflow_h
+
+#include "platform/geometry/FloatRect.h"
+#include <math.h>
+
+namespace blink {
+
+struct GlyphOverflow {
+    GlyphOverflow()
+        : left(0)
+        , right(0)
+        , top(0)
+        , bottom(0)
+        , computeBounds(false)
+    {
+    }
+
+    bool isZero() const
+    {
+        return !left && !right && !top && !bottom;
+    }
+
+    void setFromBounds(const FloatRect& bounds, float ascent, float descent, float textWidth)
+    {
+        top = ceilf(computeBounds ? -bounds.y() : std::max(0.0f, -bounds.y() - ascent));
+        bottom = ceilf(computeBounds ? bounds.maxY() : std::max(0.0f, bounds.maxY() - descent));
+        left = ceilf(std::max(0.0f, -bounds.x()));
+        right = ceilf(std::max(0.0f, bounds.maxX() - textWidth));
+    }
+
+    // If computeBounds, top and bottom are the maximum heights of the glyphs above and below the baseline, respectively.
+    // Otherwise they are the amounts of glyph overflows exceeding the font metrics' ascent and descent, respectively.
+    // Left and right are the amounts of glyph overflows exceeding the left and right edge of normal layout boundary, respectively.
+    // All fields are in absolute number of pixels rounded up to the nearest integer.
+    int left;
+    int right;
+    int top;
+    int bottom;
+    bool computeBounds;
+};
+
+} // namespace blink
+
+#endif // GlyphOverflow_h